Molecular Engineering of Copoly(ionic liquids)-Based Membranes for CO₂ Separation

The development of materials has given rise to the study and design of poly(ionic liquid)s (PILs) for making CO₂-selective membranes. The huge design space for the chemical structures of PILs provides great opportunities to further investigate the factors underlying gas permeability and selectivity. Herein, copolymerizing imidazolium-based ionic liquid (IL) monomers with two functionalized monomers of acrylamide (AM) and butyl acrylate (BA) based on free radical polymerization was conducted, and the effect of the chemical structures for PIL-based copolymers on their performances of derived membranes for CO₂/N₂ separation was evaluated. Nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy analysis confirmed the successful synthesis of copoly(ionic liquids) (co-PILs) with the designed chemical structures. The co-PIL-based composite membranes were fabricated by coating the copolymer solutions on the surface of a commercial polysulfone (PSF) membrane. It was found that the best composite membranes present significantly enhanced CO₂ permeance (76 GPU) and CO₂/N₂ selectivity (53) by 262% and 61% compared to pure PSF membranes. The proposed coating method using co-PILs provides a facile solution to improve the CO₂ separation membrane performance. Therefore, molecular engineering of the chemical structures for poly(ionic liquids) opens a venue to develop high-performance co-PIL-based membranes for potential CO₂ capture from flue gases.